Silicon-containing films are used for a wide variety of applications in the semiconductor industry. Silicon-containing films include silicon films such as epitaxial silicon, polycrystalline silicon (poly-Si), amorphous silicon, epitaxial silicon germanium (SiGe), silicon germanium carbide (SiGeC), silicon carbide (SiC), silicon nitride (SiN), silicon carbonitride (SiCN), and silicon carboxide (SiCO). As circuit geometries shrink to ever smaller feature sizes, lower deposition temperatures are preferred, for example because of introduction of new materials into semiconductor devices and reduction of thermal budgets of shallow implants in source and drain regions. Moreover, it is evident that non-selective (blanket) and selective deposition of silicon-containing films will be needed for future devices.
Epitaxial silicon deposition is a process where the crystal lattice of the bulk silicon is extended through growth of a new silicon-containing film that may have a different doping level than the bulk. Matching target epitaxial film thickness and resistivity parameters is important for the subsequent fabrication of properly functioning devices. Prior to depositing a silicon-containing film on a substrate, for example epitaxial silicon or epitaxial silicon germanium films on a silicon substrate, it may be required to remove a native oxide layer from the surface of the substrate in order to deposit a high quality epitaxial film. A native oxide layer that is typically a few to several Angstroms (Å) thick, forms easily on clean silicon surfaces, even at room temperature and atmospheric pressure. If the substrate is not cleaned prior to depositing a silicon-containing film on the substrate, i.e., all oxygen and other contaminants removed from the substrate surface, the subsequently deposited silicon-containing film will contain defects that can lead to a high leakage current through the film and cause the microelectronic device to not perform optimally.
Similarly, a poly-Si film can be deposited directly on a poly-Si film to form an electrical contact. Because other processing typically occurs between the poly-Si deposition steps, the substrates (wafers) can be removed from the processing system between the deposition steps, which can form a native oxide layer on the substrates. If the native oxide layer is not removed prior to depositing the poly-Si film, the resulting contact can have high electrical resistance.
Traditionally, a high-temperature anneal of above 900° C. in a hydrogen atmosphere is used in (vertical) batch-type processing systems to remove a native oxide layer from substrates and clean the substrates of other impurities prior to a deposition process. However, such a high-temperature process does not meet current or future thermal budget needs for many advanced processes. For example, it is well known that current gate lengths and modern microelectronic structures limit devices to a reduced thermal budget. As an alternative to high-temperature annealing in a hydrogen atmosphere, plasma processing has been found to allow lowering of the substrate temperature during processing. However, exposure of the substrate to a plasma source can result in damage to the substrate. Moreover, use of a plasma has been suggested to reduce an oxide removal temperature to a level equal to a temperature of subsequent processing steps. However, the present inventors have recognized that this places an undesirable restriction on the temperature of processing steps.